1. Field of the Invention
The present invention relates to thermostats and to controllers for heating systems, particularly for solar heating systems, in which a fluid circulation device is to be operated in response to the sensed differential temperature between fluids at two different localities.
2. Description of the Prior Art
The prior art is generally cognizant of nonelectronic controllers for solar heating systems, some of which are responsive to differential temperatures. U.S. Pat. No. 2,396,338 describes a radiation heating and cooling system which includes a differential temperature responsive device, constructed using fluid charged bulbs and bellows constructions, to sense temperature. U.S. Pat. No. 3,598,104 disloses a heating system for swimming pools using a surface temperature sensor, a subsurface temperature sensor and a comparator for comparing the voltage produced therebetween with a standard to operate a water circulation pump. U.S. Pat. Nos. 3,295,353 and 3,768,059 show other differential temperature responsive devices. U.S. Pat. Nos. 3,725,644 and 3,857,285 show other electronic temperature responsive devices.